Generally, a transistor includes a gate that functions as a transistor electrode. The gate structure may be formed to include a gate insulating film and a poly-silicon film and may be provided on a semiconductor substrate corresponding to an active region, which is defined by device isolation regions.
As the requirement for more highly integrated semiconductor devices has increased, patterns of the devices, i.e., the widths and spaces between word and bit lines, have become smaller. In particular, the gate channel lengths are decreasing as the design rule of the gate becomes more highly integrated.
Such short channel construction typically improves transistor response speed. However, because the margins for the source/drain regions formed at both sides of the gate are reduced when the channel length is shortened, a significant leakage current is generated when the gate voltage is off. Moreover, the shortened channel characteristic and the increased leakage current contribute to a deterioration of a threshold voltage characteristic and a channel current characteristic of the device.